共查询到20条相似文献,搜索用时 31 毫秒
1.
A. M. Garrido Pedrosa M. J. B. Souza D. M. A. Melo A. S. Araujo 《Journal of Thermal Analysis and Calorimetry》2007,87(2):351-355
The thermo-programmed reduction study of
Pt/WOx–ZrO2 materials
prepared with different tungsten loading were performed by thermogravimetry.
The samples were synthesized by impregnation method and calcined at 600, 700
and 800°C. The characterizations of both un-calcined and calcined materials
were carried out using different techniques: thermal analysis (TG and DTA),
X-ray diffraction (XRD) and thermo-programmed reduction (TPR). TG and DTA
analysis of un-calcined were used to determination of calcination temperatures
of the samples. XRD diffractograms were useful to help us in the determination
of phase presents. TPR profiles showed between three and four events at different
temperatures attributed to platinum reduction and the different stages of
tungsten specie reduction. 相似文献
2.
L. A. Dunyushkina A. I. Vshivkova A. A. Pankratov B. D. Antonov V. P. Gorelov 《Russian Journal of Electrochemistry》2010,46(7):767-773
The surface of ceramic electrolyte ZrO2 + 9 mol % Y2O3, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of
ZrO2, Y2O3, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing.
The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance
spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO2, Y2O3, and YSZ films to the polarization resistance of silver electrode was studied. 相似文献
3.
N. V. Lyskov Yu. G. Metlin K. I. Astaf’eva Yu. D. Tret’yakov L. S. Leonova Yu. A. Dobrovol’skii 《Russian Journal of Electrochemistry》2007,43(4):390-397
Composites ZrO2-(Bi2CuO4+ 20 wt % Bi2O3) (50–80 vol % ZrO2) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO2 of a monoclinic modification, Bi2CuO4, and solid solution Bi2?x Zr x O3 + x/2 and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 104 Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ~0.01 S cm?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO2 and 50 vol % (Bi2CuO4 + 20 wt % Bi2CuO4) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10?8 mol cm?2 s?1, testifying that these materials may be used as gas-separating membranes. 相似文献
4.
Jinshu Wang Yuntao Cui Hongyi Li Zhenzhen Wang Kelin Huang Guosong Sun 《Research on Chemical Intermediates》2010,36(1):17-26
Based on anodic aluminum oxide (AAO) templates prepared in different acidic solutions, highly ordered aligned titania nanotubes
array films have been successfully prepared by the liquid phase deposition method. The effect of AAO template type on the
microstructure of titania film have been studied. Using the template with a certain volume fraction of Al2O3 (less than 0.71), ordered aligned titania nanotubes were obtained, characterized with an outer diameter of 200 nm and an
inner diameter of 100 nm, respectively. However, titania existed as ordered aligned nanorods with the diameter of 100 nm when
the template with large volume fraction of Al2O3 (larger than 0.71) was used. TiO2 thin films calcined at 400°C for 4 h have an anatase phase and exhibit good photocatalytic activity, i.e., 75% methylene
blue could be degraded under ultraviolet irradiation for 2 h. 相似文献
5.
A. A. Shutilov G. A. Zenkovets S. V. Tsybulya V. Yu. Gavrilov G. N. Kryukova 《Kinetics and Catalysis》2012,53(3):409-418
The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO2 and CuO/(CeO2-TiO2) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO2 catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu2+ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO2 (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO2-TiO2) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO2 catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO2-TiO2) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO2. 相似文献
6.
K. S. Dhindsa A. Kumar G. A. Nazri V. M. Naik V. K. Garg A. C. Oliveira P. P. Vaishnava Z. X. Zhou R. Naik 《Journal of Solid State Electrochemistry》2016,20(8):2275-2282
We have studied LiFePO4/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO4 phase, all the samples show a varying amount of in situ Fe2P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. The amount of Fe2P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO4/C sample calcined at 700 °C which contains ~15 wt% Fe2P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g?1 at a rate of 1 C, 121 mA h g?1 at 10 C (~70 % of the theoretical capacity of LiFePO4), and excellent cycleability. Although further increase in the amount of Fe2P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li+ diffusion coefficient (~1.3?×?10?13 cm2 s?1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe2P for obtaining the best capacity for the high power batteries. 相似文献
7.
G. A. Zenkovets Yu. Yu. Tanashev V. V. Danilevich S. V. Tsybulya V. Yu. Gavrilov A. A. Shutilov V. N. Parmon 《Kinetics and Catalysis》2010,51(3):444-448
The physicochemical properties of titania (anatase) prepared from hydrated titanium dioxide by centrifugal thermal activation
(CTA) at 140–700°C were studied. It was found that the microstructure and the texture parameters of anatase prepared by the
above method were considerably different from those of the samples prepared by the traditional thermal decomposition of titanium
hydroxide. The conditions of centrifugal activation exerted a considerable effect on the structure and the texture parameters
of the resulting anatase. The crystal structure of anatase prepared at a temperature lower than 650°C was imperfect, and it
approached a regular structure only at a temperature of >650°C. At temperatures higher than 300°C, the samples of TiO2 prepared using CTA were characterized by higher specific surface areas, fine pore structures, and comparable mesopore volumes,
as compared with the samples prepared by commonly used synthetic methods. 相似文献
8.
Takeshi Miki Kaori Nishizawa Eiji Watanabe Hiroshi Taoda 《Research on Chemical Intermediates》2009,35(3):257-262
To obtain porous TiO2 film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous
TiO2 film was fabricated by the dip-coating technique on glass substrates using this solution. The TiO2 film was calcined at 500 °C. The maximum thickness of the film from one-run dip-coating was ca. 740 nm. The film was composed
of nanosized particle and pores. The porosity of the TiO2 film was increased by addition of trehalose dihydrate to the sol. The porous TiO2 films were calcined at different temperatures. The effects of calcination temperature on the microstructure of the porous
TiO2 film were investigated. The porous film prepared from sol containing trehalose still kept the porous structure after calcination
at 950 °C. The phase transition temperature of the film from anatase to rutile was shifted from 650 to 700 °C by addition
of trehalose to the sol. 相似文献
9.
Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present
review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported
on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina.
The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance
also depends on the crystal structure of Ni–Ce–ZrO2. For example, nickel catalysts co-precipitated with Ce0.8Zr0.2O2 having cubic phase gave synthesis gas with CH4 conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO2 having tetragonal phase (Ce0.8Zr0.2O2) or mixed oxide phase (Ce0.5Zr0.5O2) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst
is attributed to a combination effect of nano-crystalline nature of cubic Ce0.8Zr0.2O2 support and the finely dispersed nano size NiO
x
crystallites, resulting in the intimate contact between Ni and Ce0.8Zr0.2O2 particles. The Ni/Ce–ZrO2/θ–Al2O3 also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant
deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO2 resulting in the existence of stable NiO
x
species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results
further confirmed that NiO
x
formation was more favorable than NiO or NiAl2O4 formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support.
Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO2/CH4 ratio and H2O and/or O2 addition were also examined. 相似文献
10.
B. Szczepaniak J. Goralski J. Grams W. Maniukiewicz T. Paryjczak 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(12):1992-1996
A series of ZrO2-TiO2 mixed oxides with different weight ratios (5, 20, and 30% ZrO2) were prepared by wet impregnation of TiO2-P25 Degussa with certain amounts of ZrO(NO3)2·6H2O (Fluka) dissolved in deionised water. The samples were characterized by the XRD,
,
,
, and BET methods. An increase in ZrO2 content shifted the phase transition temperature (anatase into rutile) toward higher temperatures. X-ray diffraction using
an Anton Paar XRK900 reactor chamber indicated that, in the case of samples containing ZrO2, an additional diffraction peak appeared after cooling down to 25°C. This peak could be attributed to a polymorph of TiO2 such as in the single crystal of anatase or hexagonal form of TiO2 which appears in the presence of ZrO2. Generally, the preparation of dioxide systems can modify the properties of pure compounds or generate new catalytic sites
as a result of strong interaction between ZrO2 and TiO2 oxides. The binary systems exhibit advantages like strong acidity, extended specific surface area, and high thermal stability
in comparison with TiO2.
The article is published in the original. 相似文献
11.
Phase equilibria in the system CaO-CoO-Co2O3-MnO-MnO2 at 700–1200°C in air were studied on the basis of published data and proper experiments. No new compounds were found. The
results are presented in the form of 13 isothermal sections of the phase diagram. 相似文献
12.
A. L. Zharnyl’skaya V. V. Vol’khin H. Reuther 《Russian Journal of Applied Chemistry》2009,82(8):1364-1369
Samples of a precursor for an aluminum oxide ceramics reinforced with zirconium oxide were synthesized by hydrolysis of various
aluminum salts in the presence of a ZrO2 sol under conditions of urea decomposition at 90°C and pH < 4 maintained, with hydrolysis products deposited onto the surface
of ZrO2 sol particles. It was found that the nature of a salt anion affects the interaction of hydrolysis products of the aluminum
cation with the surface of ZrO2 sol particles. The structure of products formed in thermal treatment of samples of a precursor for Al2O3-ZrO2 (T = 1250°C) was characterized by X-ray phase analysis and scanning electron microscopy. The phase transition temperatures of
the oxides Al2O3 and ZrO2 contained in the precursor were estimated using the results of thermal analysis of the samples in the temperature range 20–1300°C. 相似文献
13.
L. A. Dunyushkina S. V. Plaksin A. A. Pankratov L. A. Kuz’mina V. M. Kuimov V. P. Gorelov 《Russian Journal of Electrochemistry》2011,47(11):1274-1280
CaZrO3 films are studied that were obtained on ceramic supports of solid electrolyte of ZrO2 + 9 mol % Y2O3 (YSZ, yttria stabilized zirconia) from alcohol solutions of zirconium oxychloride and calcium nitrate using the method of
dipping with the following drying and annealing. The thickness and morphology of films depend on the concentration of the
film-forming solution. Vickers microhardness of the CaZrO3 films was determined. The impedance spectroscopy method was used to study conductivity of films at the temperature of 400–600°C
by comparison of impedance spectra of clean supports and supports with a film coating. 相似文献
14.
H. Y. Yue W. D. Fei Z. J. Li L. D. Wang 《Journal of Sol-Gel Science and Technology》2007,44(3):259-262
Zinc nitrate and citric acid were used to prepare ZnO sol. ZnO and ZnAl2O4 coated aluminum borate whiskers were separately prepared by a sol–gel process. The results show that ZnO forms when ZnO xerogel
is calcined at 500 °C and it does not undergo any phase transformation in the range of 500 and 1000 °C during calcinations.
In ZnO xerogel coated aluminum borate whiskers system, a large amount of heat, gas and pores are produced during the heating
process. When ZnO xerogel coated aluminum borate whiskers are calcined at 500 °C, ZnO can be uniformly coated on the surface
of the whikers and the coated whiskers can be easily dispersed in distilled water through an ultrasonic vibration apparatus.
During the calcination of ZnO coated whiskers at 1000 °C, ZnO reacts with the whiskers and ZnAl2O4 forms on the surface of aluminum borate whiskers. 相似文献
15.
Zh. G. Bazarova A. I. Nepomnyashchikh A. A. Kozlov V. D. Bogdan-Kurilo B. G. Bazarov A. K. Subanakov R. V. Kurbatov 《Russian Journal of Inorganic Chemistry》2007,52(12):1971-1973
The subsolidus region of the Li2O-MgO-B2O3 system has been studied by X-ray powder diffraction and differential thermal analysis. Isothermal sections at 500–550 and 650–700°C have been designed. The following complex borates have been found to form: at 500–550°C, Li2MgB2O5 and LiMgBO3 are formed; at 650–700°C, a new phase Li4MgB2O5 is formed along with LiMgBO3; and at 5500–600°, Li2MgB2O5 is formed. 相似文献
16.
Pradeepan Periyat K. V. Baiju P. Mukundan P. Krishna Pillai K. G. K. Warrier 《Journal of Sol-Gel Science and Technology》2007,43(3):299-304
Nanocrystalline sol–gel derived titania doped with ceria (1, 2, 5 and 10-mole%) has been prepared from titanyl oxysulphate.
The titania doped with 5-mole% CeO2 after calcining to 500 °C, possesses specific surface area of 97 m2 g−1 and has anatase phase stability up to 900 °C. Moreover it retains a surface area of 37 m2 g−1 at 700 °C. In comparison, the undoped calcined material has anatase stability only up to 700 °C and specific surface area
only 48 m2 g-1 and 6 m2 g-1 at 500 °C and 700 °C, respectively. The diffuse reflectance spectra show that, as the cerium content increases, the absorption
undergoes a red shift and reaches the visible range. The exceptionally high phase stability, crystallinity and high surface
area are due to the extremely fine particle size and effective doping achieved by the specific synthesis method. The results
based on X-ray diffraction, specific surface area and diffuse reflectance spectra indicated that the maximum threshold limit
of doping is up to a value of 5-mole%. 相似文献
17.
Junseo Choi Ji-Young Ban Suk-Jin Choung Jinsoo Kim Haznan Abimanyu Kye Sang Yoo 《Journal of Sol-Gel Science and Technology》2007,44(1):21-28
Mesoporous TiO2/γ-Al2O3 composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules
can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of
the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH3 decomposition, TiO2/γ-Al2O3 granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO2/γ-Al2O3 granules using titania made by hydrothermal method had comparable performance in NH3 decomposition. 相似文献
18.
Nanocrystalline TiO2 powders in the anatase, rutile, and mixed phases prepared by hydrolysis of TiCl4 solution were of ultrafine size (<7.2 nm) with high specific surface areas in the range 167 to 388 m2/g. In the photocatalytic degradation of phenol as model reaction, the photocatalytic properties of TiO2 nanoparticles were evaluated by use of UV–vis absorption spectroscopy and total organic carbon (TOC) content. The synthetic
mixed-phase TiO2 powder calcined at 400 °C had higher activity than pure anatase or rutile; it degraded more than 90% phenol to CO2 (evaluated by TOC) after irradiation with near UV light for 90 min at a catalyst loading of 0.4 g/L. The TOC results indicated
that rutile TiO2 crystallites of particle size 7.2 nm resulted in much better photocatalytic performance than particles of larger size. This
result suggested that some intermediates, not determined by UV–vis absorption spectroscopy, existed in the solution after
the photocatalytic process over the rutile TiO2 photocatalysts of larger crystallite size. 相似文献
19.
R. G. Pavelko A. A. Vasil’ev V. G. Sevast’yanov F. Gispert-Guirado X. Vilanova N. T. Kuznetsov 《Russian Journal of Electrochemistry》2009,45(4):470-475
The thermal stability of synthesized and commercial SnO2, ZrO2, and SiC nanopowders is compared. The crystallite growth rate during the isothermal annealing of the materials at 700°C for 30 h is evaluated. The crystallites’ average size was determined by X-ray phase analysis (using the Scherrer method). The effect of impurity content on the kinetics of crystallite growth is studied for the synthesized SnO2 and ZrO2. Semiconductor and thermocatalytic sensors, based on the synthesized and commercial materials, are manufactured. The long-term stability of the sensors’ signal is compared with the thermal stability of the nanopowders. 相似文献
20.
A H3PW12O40/ZrO2 catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO3 or H2WO4, enhanced the catalytic performances of the supported ZrO2. The mesoporous structure of H3PW12O40/ZrO2 was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m2/g. The strong acidity of H3PW12O40/ZrO2 was confirmed by the desorption peak observed at 415 °C in NH3 temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO2/N2 volumetric flow rate ratios (CO2/N2?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO2/N2?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10?3 min?1) and activation energy (Ea?=?15.54 kJ/mol) at 170 °C with CO2/N2?=?1/7 which were favorable for DMC formation. 相似文献